Total hip arthroplasty (THA) using metallic hip prostheses has been successfully performed since the early 1960""s and is now a routine procedure. The use of cement to fill the space between the bone and the prosthesis, and bony ingrowth, where the bone grows into a porous prosthesis, have been the two primary methods of fixation used. For the structure of the femur before THA, the load distribution can be essentially resolved into an axial component, two bending moments and a torsional moment which depend upon the leg stance. The distribution of these load components is changed after THA. The current methods of fixation allow for transfer of axial loads to the bone mainly through shear stresses at the bone-implant interface. (The muscles attached to the femur transfer load and moments as before THA.) The bending moment is effectively transferred to the bone, primarily through contact between the prosthesis and bone in two or more localized regions. In addition, the great disparity in the stiffness of a metallic prosthesis and the surrounding bone reduces bending displacements changing the bending moment distribution in the surrounding bone. The current procedure although very successful in the older population has a relatively lower rate of success in the younger population.
A major cause of failure of the prosthesis using the current design methodology is associated with the resorption of the bone which can be the result of stress shielding of the bone caused by the use of a stiff prosthesis as well as the increase in shear stresses at the bone-prosthesis interface. The effective transfer of loads will depend on the stiffness of the prosthesis and the bone-prosthesis interface as well as physiological loading of the proximal end.
The conventional approach for providing a hip prosthesis incorporates the use of a stem mounted in the femur. It would be desirable if a hip prosthesis could be provided which is stemless.
An object of this invention is to provide a stemless hip prosthesis.
A further object of this invention is to provide such a stemless hip prosthesis which can easily be applied while still maintaining its effectiveness.
In accordance with this invention the prosthesis is mounted to the femur through the use of cables. Preferably the cable or cables are wrapped around a portion of the femur and a portion of the prosthesis.